Prescribing for Presbyopia
The Year of Custom Soft Lenses
By Craig W. Norman, FCLSA
Many items of interest were presented at the recent 2011 Global Specialty Lens Symposium (GSLS) in Las Vegas, but none greater than the discussions regarding custom soft contact lenses. U.S.-based GP and specialty lens manufacturers have embraced this category by offering new lens designs, and at the GSLS many presentations described the use of custom soft lenses for out-of-the-routine refractive errors such as high astigmatism and even irregular corneas. Of particular interest to me were the discussions regarding the use of custom designs for presbyopia (Table 1).
New Material Introduction
There was a lot of the buzz at the GSLS regarding the newly FDA-approved Contamac Definitive silicone hydrogel (SiHy) material. No fewer than four companies discussed the launch of presbyopic designs in this latheable SiHy material. Many designs that were previously available only in standard hydrogel materials are now being offered in this new SiHy material with an emphasis on higher oxygen transmissibility for improved corneal health and availability in frequent lens replacement programs.
Get the Perfect Sag Height
So what's the big deal about custom soft lenses for presbyopia? For me, better control of lens positioning is the most important. Placing the correct multifocal optics in front of a patient's line of sight at the right time is the key to presbyopic soft lens visual success. Unfortunately, if a design has only one (or two) base curves and one diameter, this may be difficult to achieve.
But now, by changing to a custom base curve, a custom diameter, or both, sag heights can be adjusted to achieve the best fit possible. This is especially important for patients who have a horizontal visible iris diameter that is smaller or larger than normal and necessitates a unique base curve/diameter configuration.
Get the Perfect Zone Size
Most soft lens multifocals employ center-near optics that may be either spherical or aspheric and are usually available in a standard zone size. Custom designs allow us to vary this size depending on the patient's line of sight and pupil size/dynamics. Minor changes in near zone width can play a big role in improving either distance or near vision. Here's where the laboratories' design consultants can be very helpful in selecting the proper zone size for a specific situation.
Certainly, custom designs will provide almost unlimited combinations of sphere, cylinder, and axis along with varying add powers. But what else might we see in the near future?
Previous attempts to market soft, segmented bifocals have met with practitioner resistance, but hallway conversations at the GSLS have convinced me that this option is soon to return. Earlier-generation translating soft lens bifocals demonstrated excellent vision but at the expense of a higher risk to corneal health. We may now be able to lower that risk to currently acceptable levels.
Also, what about decentered optics in spherical (or even toric) prism-ballasted designs? Or peripheral curve alterations for better lens stabilization?
Stay tuned—custom soft lenses may be one of the most exciting entries in presbyopia yet. CLS
Craig Norman is director of the Contact Lens Section at the South Bend Clinic in South Bend, Indiana. He is a fellow of the Contact Lens Society of America and is an advisor to the GP Lens Institute. He is also a consultant to B+L. You can reach him at email@example.com.